다공질 ZnO의 전기적 특성, 환원성 가스 감응 특성 및 습도의 영향

윤당혁,최경만 한국세라믹학회 1995 한국세라믹학회지 Vol.32 No.11

The electrical conductivity, flammable gas response and their humidity effect of porous ZnO, added with 5wt% corn starch as the fugitive phase, were examined. Porous ZnO showed different conductivity curves during increasing and decreasing temperature, and its electrical conductivity decreased rapidly by desorption of OH- between 20$0^{\circ}C$ and 35$0^{\circ}C$ when the temperature increased in dry air. The CO gas sensitivity of starchadded ZnO samples was higher than that of ZnO without starch addition. The sensitivity of porous, starchadded ZnO to 200ppm CO gas was much less in humid atmosphere than in dry atmosphere since water vapor increased the conductivity of porous ZnO in air, but decreased the conductivity in CO. Maximum sensitivity to 200 ppm CO gas balanced by air was about 100 in dry atmosphere and about 15 in RH 23% atmosphere.

Tetragonality of barium titanate powder for a ceramic capacitor application

윤당혁 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.4

Although nano-sized barium titanate powder (BaTiO3) with a high tetragonality (large c/a) is essential to enhance the volumetric efficiency of multi-layer ceramic capacitors (MLCCs) in industry, the tetragoanlity diminishes with a decrease in particle size and disappears below a critical particle size. Many researchers have investigated an understanding of the relationship between particle size and the tetragonality of BaTiO3 and tried to increase this value while maintaining the particle size as small as possible. Recent experimental results, including ours, on critical particle sizes and their tetragonality values of fine BaTiO3 powders are reviewed in this paper. Although nano-sized barium titanate powder (BaTiO3) with a high tetragonality (large c/a) is essential to enhance the volumetric efficiency of multi-layer ceramic capacitors (MLCCs) in industry, the tetragoanlity diminishes with a decrease in particle size and disappears below a critical particle size. Many researchers have investigated an understanding of the relationship between particle size and the tetragonality of BaTiO3 and tried to increase this value while maintaining the particle size as small as possible. Recent experimental results, including ours, on critical particle sizes and their tetragonality values of fine BaTiO3 powders are reviewed in this paper.

Improved field emission stability and uniformity of printed carbon nanotubes prepared using high energy-milled glass frit

윤당혁,Young Chul Choi 한국물리학회 2013 Current Applied Physics Vol.13 No.7

Stable and uniform electron field emitters were fabricated by the screen-printing of a carbon nanotube (CNT) paste. The CNT paste was prepared by mixing thin multi-walled CNTs, organic binder and glass frits in terpineol followed by three-roll milling. The paste was screen-printed onto an indium tin oxide (ITO)-coated glass substrate and exposed to firing. The emitters formed by the adhesive tape treatment of the printed pastes generally showed non-uniform heights of emitting tips due to the large-sized glass frit distributed in the paste. On the other hand, small glass frits with a uniform particle size distribution could be obtained by high energy milling. In addition, the CNT paste prepared using the high energymilled glass frits showed very uniform tip heights. The uniform CNT tip height was found to play an important role in acquiring the long-term emission stability and uniformity of field emitters.

제조방법에 따른 Al2O3-SiCw 복합체의 특성

이대엽,윤당혁 한국세라믹학회 2014 한국세라믹학회지 Vol.51 No.5

Al2O3-SiC composites reinforced with SiC whisker (SiCw) were fabricated using three different methods. In the first, Al2O3-SiCwstarting materials were used. In the second, Al2O3-SiCw-SiC particles (SiCp) were used, which was intended to enhance the mechanicalproperties by SiCp reinforcement. In the third method, reaction-sintering was used with mullite-Al-C-SiCw starting materials. After hotpressingat 1750oC and 30 MPa for 1 h, the composites fabricated using Al2O3-SiCw and Al2O3-SiCw-SiCp showed strong mechanicalproperties, by which the effects of reinforcement by SiCw and SiCp were confirmed. On the other hand, the mechanical properties ofthe composite fabricated by reaction-sintering were found to be inferior to those of the other Al2O3-SiC composites owing to itsrelatively lower density and the presence of γ-Al2O3 and γ-Al2.67O4. The greatest hardness and K1C were 20.37 GPa for the compositefabricated using Al2O3-SiCw, and 4.9 MPa·m1/2 using Al2O3-SiCw-SiCp, respectively, which were much improved over those from the monolithic Al2O3.

제조방법에 따른 Al₂O₃-SiC_w 복합체의 특성

이대엽,윤당혁,Lee, Dae-Yeop,Yoon, Dang-Hyok 한국세라믹학회 2014 한국세라믹학회지 Vol.51 No.5

$Al_2O_3$-SiC composites reinforced with SiC whisker ($SiC_w$) were fabricated using three different methods. In the first, $Al_2O_3-SiC_w$ starting materials were used. In the second, $Al_2O_3-SiC_w$-SiC particles ($SiC_p$) were used, which was intended to enhance the mechanical properties by $SiC_p$ reinforcement. In the third method, reaction-sintering was used with mullite-Al-C-$SiC_w$ starting materials. After hot-pressing at $1750^{\circ}C$ and 30 MPa for 1 h, the composites fabricated using $Al_2O_3-SiC_w$ and $Al_2O_3-SiC_w-SiC_p$ showed strong mechanical properties, by which the effects of reinforcement by $SiC_w$ and $SiC_p$ were confirmed. On the other hand, the mechanical properties of the composite fabricated by reaction-sintering were found to be inferior to those of the other $Al_2O_3$-SiC composites owing to its relatively lower density and the presence of ${\gamma}-Al_2O_3$ and ${\gamma}-Al_{2.67}O_4$. The greatest hardness and $K_{1C}$ were 20.37 GPa for the composite fabricated using $Al_2O_3-SiC_w$, and $4.9MPa{\cdot}m^{1/2}$ using $Al_2O_3-SiC_w-SiC_p$, respectively, which were much improved over those from the monolithic $Al_2O_3$.

Densification of SiCf/SiC composites by electrophoretic infiltration combined with ultrasonication

길건영,윤당혁 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.4

An electrophoretic deposition (EPD) technique was used to infiltrate a SiC-based matrix phase into the fine voids of a TyrannoTM-SA SiC preform with/without the application of ultrasound. The zeta potential and viscosity of the suspension were controlled to achieve a uniform and simultaneous deposition of all constituents. EPD was performed under a 10 V DC electric field for 30 minutes after adjusting the suspension pH to 3, in which the zeta potentials for all constituents were ≥ + 40mV. The composites fabricated by EPD combined with ultrasonication showed a much higher degree of infiltration due to the minimized surface sealing effect than those by EPD only. After hot pressing at 1750 oC for 2 hours, the density of the composites by the combined process was 99.5%, which is the highest SiCf/SiC density ever reported.

Interfacial Microstructure and Shear Strength of Reactive Air Brazed Oxygen Transport Membrane Ceramic–Metal Alloy Joints

와히드무하마드,윤당혁,카티라주,김세영,송광섭,유지행 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.1

To fabricate a multi-layered structure for maximizing oxygen production, oxygen transport membrane (OTM)ceramics need to be joined or sealed hermetically metal supports for interfacing with the peripheral components ofthe system. Therefore, in this study, Ag–10 wt% CuO was evaluated as an effective filler material for the reactiveair brazing of dense Ce0.9Gd0.1O2–δ – La0.7Sr0.3MnO3±δ (GDC–LSM) OTM ceramics. Thermal decomposition in airand wetting behavior of the braze filler was performed. Reactive air brazing was performed at 1050 °C for 30 minin air to join GDC–LSM with four different commercially available high temperature-resistant metal alloys, suchas Crofer 22 APU, Inconel 600, Fecralloy, and AISI 310S. The microstructure and elemental distribution of theceramic-ceramic and ceramic-metal interfaces were examined from polished cross-sections. The mechanical shearstrength at room temperature for the as-brazed and isothermally aged (800 °C for 24 h) joints of all the samples wascompared. The results showed that the strength of the ceramic-ceramic joints was decreased marginally by aging;however, in the case of metal-ceramic joints, different decreases in strengths were observed according to the metalalloy used, which was explained based on the formation of different oxide layers at the interfaces.

Fabrication of SiCf/SiC Composites using an Electrophoretic Deposition

이종현,길건영,윤당혁 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.5

Continuous SiC fiber-reinforced SiC composites (SiCf/SiC) were fabricated by electrophoretic deposition (EPD). Nine types of slurries with different powder contents, binder resin amounts and slurry pH were deposited on TyrannoTM-SA fabrics by EPD at 135 V for ten minutes to determine the optimal conditions. Further EPD using the optimum slurry conditions was performed on fabrics with four different pyrolitic carbon (PyC) thicknesses. The density of the hot-pressed composites decreased with increasing PyC thickness due to the difficulty of infiltrating the slurry into the narrow gaps between the fibers. On the other hand, the mechanical strength increased with increasing PyC thickness despite the decrease in density, which was explained by the enhanced crack deflection with increasing PyC thickness. The SiCf/SiC composites showed the highest density and flexural strength of 94% and 342 MPa, respectively, showing EPD as a feasible method for dense SiCf/SiC fabrication.

SiC_f/SiC 복합체의 특성에 미치는 열간가압소결 조건의 영향

노비얀토 알피안,윤당혁,Noviyanto, Alfian,Yoon, Dang-Hyok 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.5

Continuous SiC fiber-reinforced SiC-matrix composites ($SiC_f$/SiC) had been fabricated by electrophoretic infiltration combined with ultrasonication. Nano-sized ${\beta}$-SiC added with 12 wt% of $Al_2O_3-Y_2O_3$ additive and Tyranno$^{TM}$-SA3 fabric were used as a matrix phase and fiber reinforcement, respectively. After hot pressing at 5 different conditions, the density, microstructure and mechanical properties of $SiC_f$/SiC were characterized. Hot pressing at relatively severe conditions, such as $1750^{\circ}C$ for 1 and 2 h, resulted in a brittle fracture behavior due to the strong fiber-matrix interface in spite of their high flexural strength. On the other hand, toughened $SiC_f$/SiC composite could be achieved by hot pressing at milder condition because of the formation of weak interface in spite of the decreased flexural strength. These results proposed the importance of weak fiber-matrix interface in the fabrication of ductile $SiC_f$/SiC composite.

항공 우주용 CMC(Ceramic Matrix Composite) 치밀화 기술

박지연,김원주,윤당혁 한국세라믹학회 2009 세라미스트 Vol.12 No.1